1. Field of the Invention
The present invention relates generally to the field of optical communication and, more specifically, to an improved optical rotary communication system that provides optical communication offset from the rotary axis on applications such as spacecrafts and gimbals.
2. Description of the Related Art
In recent years, the use of optical communication systems, such as fiber optic signal transmission systems, has increased. One problem confronted over the years has been the effective transmission of optical signals onto or off of rotating devices in what has been referred to as optical rotary joints. This problem exists for example in the context of spacecrafts, gimbals, or missile heads where one portion rotates relative to the other portion. In those situations, like others, the design of communication apparatus commonly includes a rotating device that lies co-axial with a non-rotating device and an axial portion intermediate the rotating and non-rotating devices.
One solution to the problem is to provide an optical rotary joint that transmits an optical signal between the interfacing surfaces of rotating and non-rotating members outside of the rotating axis to thereby allow the axial portion between the two members to remain free for other purposes. One example of this type of optical rotary joint is shown in Einhorn et al., Off Axis Optical Communication System, U.S. Pat. No. 4,753,506, which is hereby expressly incorporated by reference herein. An optical rotary joint includes first and second communication surfaces on spun and de-spun portions, respectively. A transmitter mechanism on one of the communication surfaces creates a plurality of communication paths which transmit an optical signal to the other communication surface. The communication paths form overlapping elliptical areas on the second communication surface to form a continuous ring for reception of the optical signal by a detector placed on the second communication surface. Alternatively, a single transmitter on the first communication surface transmits the optical signal through a single communication path and creates a single elliptical area on the second communication surface. The second communication surface has a plurality of space detectors mounted thereon which are spaced apart by a distance slightly less that the major axis of the elliptical area. In this arrangement, at least one of the spaced detectors lies within the elliptical area, thereby allowing constant transmission of the optical signal across the optical rotary joint.
The plurality of transmitters and the plurality of detectors shown in the Einhorn et al. patent are each activated at all times to facilitate communication of the optical signal across the optical rotary joint at all points in the rotation of the spun portion. In the embodiment utilizing a plurality of transmitters, the corresponding detector is encompassed by at most two elliptical areas projected onto the second communication surface at any point in the rotation. The remaining transmitters are generating communication paths which go undetected until the detector enters the projected elliptical area. Similarly, in the multiple detector embodiment, at most two detectors are encompassed by the single area projected by the lone transmitter at any point in the rotation. The remaining detectors are activated, but have no optical signal to detect until they enter the elliptical area.
Accordingly, there is a need for an improved optical rotary joint which reduces the power consumption of the optical rotary joint.